Apparatus and methods for leak detection in bioprocessing bags

ABSTRACT

An apparatus detects a leak of an electrically conductive fluid from a disposable plastic bag used in mixing applications, such as during bioprocessing in a sterile environment. In one embodiment, the bag is associated with a sensor for detecting a leak from an interior compartment. The sensor may be arranged to detect either a leak internal to the at least two material layers of the bag or external to the outer layer, or both. Related methods are also disclosed.

This application is a continuation of International ApplicationPCT/US07/64492, filed Mar. 21, 2007, which claims the benefit of U.S.Provisional Patent App. Ser. No. 60/784,615, filed Mar. 22, 2006, thedisclosures of which are both incorporated herein by reference.

TECHNICAL FIELD

The present invention relates generally to fluid processing and, moreparticularly, to apparatus and methods for detecting leaks that mayresult during the processing of fluids under sterile conditions.

BACKGROUND OF THE INVENTION

Many manufacturers of products requiring a temporary holding, mixing orother fluid processing step as part of the manufacturing process now optto use disposable bags for holding and contacting the fluid understerile conditions instead of rigid mixing tanks or vessels.Advantageously, such bags are relatively inexpensive to manufacture,easy to transport, store, and sterilize, and can be disposed of once theoperation is complete and any product recovered. Moreover, the use ofsuch bags not only both eliminates the need for cleaning and the chancefor cross-contamination, but also reduces the overall process cost.

A frequent problem encountered by users of such bags, which aretypically made of one or more layers of thin, fluid-impervious plasticfilm, is the risk of undesirable leakage. In the case of bioprocessingapplications, such leaks result in the loss of sterility inside the bagor the release of potentially hazardous biological material. If notdetected, such leakage can thus compromise the entire mixing operationand render the end product unsuitable for use. However, early detectionof such leakage can advantageously lead to appropriate corrective actionbeing taken, such as before the end product is distributed.

Up to now, leakage in these types of processing bags has been difficultto detect in a reliable fashion. Usually, such leakage is discoveredvisually in the form of wetness on the outside surface of the bag,spills on the floor and so on. Of course, this method of detection isnot reliable, since such wetness may result from the condensation on thebag outer surface, and unidentified spills can arise from other sources.Also, many leaks cannot be detected visually if the bag is kept in theclosed non-transparent container.

In the particular case of bioprocessing, most of the biological fluidsheld, stored or processed in bags comprise liquids, such as water basedelectrolytes, that are relatively good electrical conductors. Thematerial comprising the bag, on the other hand, is typicallypolyethylene or other plastic which is very good electrical insulator.The bags containing biological fluids can have just one layer of plasticfilm or several layers of film. In the latter case, the fluid touchinglayer of the bag usually has the best leachable and extractablecharacteristics to minimize the contamination of the processed fluidwith molecules diffised out of the plastic to the fluid. This layer istypically low density polyethylene. However, this innermost layer haspoor mechanical strength, and thus one or more additional layers areadded to enhance the mechanical strength of the bag.

The external layer(s) are not supposed to touch the processed fluid butprovide for the mechanical strength of the bag. Even though those layersare also sterile on the inner side, they may leach substantial amount oforganic molecules if they contact fluid as a result of the internalleak. Consequently, the leaks that can develop in the bags can be of twotypes:

1. Internal leaks where the electrically conductive fluid in theinterior compartment of the bag through only one or several layers ofthe film but does not leak outside of the bag; or

2. External leaks, where the conductive fluid leaks to the outsidenon-sterile environment.

Both types of leaks can potentially contaminate the product in the bagand thus are highly undesirable.

Accordingly, a need exists for an expedient, yet reliable manner fordetecting either or both of these types of leaks, thereby allowing forimmediate corrective action to be taken.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the invention, an apparatusintended for use in at least temporarily holding an electricallyconductive fluid in need of processing under sterile conditions isprovided. The apparatus comprises a plastic bag having a first interiorcompartment capable of receiving the conductive fluid for processingunder sterile conditions. The apparatus further includes a rigidcontainer having a second interior compartment for at least partiallyreceiving and supporting the bag. A sensor is provided for sensing thepresence of a leak of the conductive fluid from the first interiorcompartment, which can thus be used to indicate the potential lack ofsterility in the interior compartment and allow for immediate correctiveaction.

In one embodiment, the sensor comprises first and second electrodes. Thesecond electrode is arranged external to the first interior compartmentand capable of being connected to the first electrode contacting theconductive fluid by the leak. Preferably, the sensor flirter includes agenerator of AC or DC voltage and a detector connected to the first andsecond electrodes for detecting the current flowing in the resultingcircuit in the presence of a leak.

The first electrode may project through a hermetic seal formed in thesidewall of the bag, in which case the bag may include a tubular portfor receiving the first electrode. Still more preferably, the tubularport includes a connector for allowing the first electrode to contactthe conductive fluid under sterile conditions. The rigid supportcontainer may at least partially comprises a conductive material formingthe second electrode.

In another embodiment, the bag comprises a first layer of materialarranged for forming the first interior compartment and a second layerof material adjacent the first layer of material. Preferably, the sensorcomprises first and second electrodes for positioning at least partiallybetween the first and second layers of material. Alternatively, one ofthe first and second electrodes comprises the second layer of materialof the bag.

In accordance with another aspect of the invention, a further apparatusintended for use in at least temporarily holding an electricallyconductive fluid in need of processing under sterile conditions anddetecting a leak thereof is disclosed. This apparatus comprises aplastic processing bag having a first interior compartment capable ofreceiving the conductive fluid under sterile conditions, and an at leastpartially conductive support structure includes a second interiorcompartment for at least partially receiving the plastic processing bag.An electrode connected to the conductive fluid in the first interiorcompartment is arranged to form an electrical circuit with theconductive support structure in the presence of the leak. To facilitateleak detection, a generator of AC or DC voltage and a detector fordetecting the current flow in the resulting circuit may be connected tothe electrode and the conductive support structure.

In accordance with still a further aspect of the invention, an apparatusis intended for use in at least temporarily holding an electricallyconductive fluid in need of processing and detecting a leak thereof. Theapparatus comprises a processing bag comprising a first layer offlexible material creating an interior compartment capable of receivingthe conductive fluid under sterile conditions and a second layer offlexible material adjacent the first layer. First and second electrodesarranged external to the interior compartment are arranged so as to becapable of being connected by the leak. At least the first electrodeextends at least partially between the first and second layers offlexible material.

In one embodiment, both of said first and second electrodes are betweenthe first and second layers of flexible material. However, it is alsopossible to make the second layer of flexible material and the secondelectrode unitary. The second electrode may also comprise a rigidcontainer for receiving and supporting the bag.

In accordance with yet another aspect of the invention, a method ofprocessing fluid under sterile conditions is described. The methodcomprises providing a plastic processing bag having a first interiorcompartment creating a sterile environment placing the bag in a supportstructure having a second interior compartment, providing anelectrically conductive fluid to the interior compartment, and providinga sensor for detecting the presence of a leak of the conductive fluidfrom the first interior compartment.

In one embodiment, the providing step further includes providing firstand second electrodes capable of being connected by the leak, and themethod further includes connecting a generator of AC or DC voltage and adetector for detecting current flow in the resulting circuit to thefirst and second electrodes. Preferably, the support structure is atleast partially conductive, and the step of providing first and secondelectrodes comprises providing the first electrode in contact theconductive fluid in the first interior compartment and using the supportstructure as the second electrode. In the case where the bag comprisesfirst and second layers of material, the providing step may insteadcomprise positioning the first and second electrodes external to thefirst interior compartment and at least partially between the first andsecond layers of material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a mixing arrangement including a bag ina rigid support container for possible use with fluids under sterileconditions;

FIG. 2 is a schematic diagram of a leak detection apparatus forming oneaspect of the present invention;

FIG. 3 is a schematic diagram illustrating an alternative embodiment ofthe leak detecting apparatus of FIG. 2;

FIG. 4 is a schematic diagram of a leak detection apparatus forminganother aspect of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As noted above, the present invention relates primarily to apparatus andmethods for leak detection. A particularly advantageous use of theinventive apparatus and methods is in connection with bioprocessingapplications where fluid conductors, electrically conductive biologicalfluids (typically liquids comprising or consisting essentially ofwater), are at least temporarily held in thin-walled, flexible orcollapsible vessels, such as for example disposable bags made of one ormore layers of plastic film. As noted above, this type of vessel canadvantageously be disposed of once the operation is complete and anyproduct recovered. This type of arrangement thus not only botheliminates the need for cleaning and the chance for cross-contamination,but also reduces the overall process cost.

A particularly preferred use of such a processing bag is in a fluidmixing system. As shown in FIG. 1, the bag B is positioned in theinterior compartment of a rigid container C that serves as a supportstructure. The bag B further includes an interior compartment adaptedfor receiving and at least temporarily holding an electricallyconductive fluid F and, most preferably, a biologically active liquid.The volume of the bag B is generally greater than one liter, andpreferably on the order of 10 to 1,000 liters.

Means for agitating the fluid in the bag B, such as a magnetic impellerI rotated by an external motive device D may also be provided, as shown.Alternatively or in addition, the fluid agitating means may comprise asparger (not shown) for introducing a gas into the bag B. Additionaldetails of such fluid-agitating means may be found in commonly assigned,co-pending U.S. patent application Ser. No. 11/304,417, the disclosureof which is incorporated herein by reference.

One exemplary apparatus 10 for detecting leaks in such a bag B, which isespecially important when the sterility of the interior compartment musthe maintained, is now described with reference to FIG. 2. Asillustrated, the apparatus 10 includes a leak sensor or means forsensing a leak comprising at least one (and preferably only one)electrically conductive electrode 12 associated with the bag B (which,although not shown, may include the agitating means, such as theimpeller I of FIG. 1). In this first embodiment, this electrode 12penetrates the corresponding wall of the bag B such that one end atleast partially contacts the liquid inside and the other end ispositioned external to the interior compartment. However, as will bedescribed below, it is not necessary for the electrode 12 to penetratethe sidewall of the bag B in order to make contact with the fluid F,even if the sterile conditions are to be maintained.

In this embodiment, the sensor further comprises a second electrode(alternately referred to as a conductor for purposes of clarity) alsoforming part of the sensor or means for sensing, but external to theinterior compartment of the bag B. Preferably, this second electrode orconductor comprises a conductive material forming at least part of asupportive structure for the bag B, such as a rigid container 14. Thiscontainer 14 is preferably formed entirely of a rigid, conductivematerial, such as stainless steel. The container 14 is arranged suchthat it least partially and preferably fully receives the bag B, bothwhen it is empty (that is, before the fluid is introduced) and also whenfilled. Although shown spaced apart in FIG. 2 for purposes of cleardifferentiation, it should be appreciated that, when the bag B is filledwith liquid, the interior surface of the container 14 is normally inintimate contact with external or outer surface of the bag (see, e.g.,bag B and container C in FIG. 1).

The sensor or sensing means of the apparatus 10 as illustrated forpurposes of this preferred embodiment further comprises: (1) a generator16 capable of generating DC (Direct current) or AC (Alternating current)voltage (e.g., a battery or alternator); and (2) a detector 18 capableof detecting DC or AC electric current. Suitable connections, such as bywires, interconnect the electrode 12, container 14, generator 16, anddetector 18 so as to form a circuit, the purpose of which is outlinedfurther in the following description.

In a simple embodiment, and as shown in FIG. 2, the first electrode 12comprises an elongated piece of metal material (and preferably one thatis corrosion-resistant, such as stainless steel). This electrode 12 maypenetrate through the wall via a port of the bag B. An annular hermeticseal S between the rod serving as the electrode 12 and the port of thebag B may be provided to maintain the sterile interior environmenttypically desired. However, the electrode could take any other form thatallows for the desired electrical contact with the conductor (e.g.,container 14) to be established.

In one preferred mode of use and in accordance with the practice of amethod of leak detection, the bag B is equipped with the electrode 12.As noted above, this may be accomplished by positioning the electrode 12so that it penetrates through the selected sidewall of the bag B (suchas the top wall) in a hermetic manner, as shown in FIG. 2. In any case,the result is that one end of the electrode 12 communicates with theinterior, potentially sterile environment of the bag B and is at leastpartially in contact with the conductive fluid F or liquid. In contrast,the other end of the electrode 12 projects outside of the bag B or isotherwise in communication with the external environment. As a result ofthe connection noted above, the electrode 12 forming part of the sensorfor purposes of this preferred first embodiment of the apparatus 10allows electrical contact to be established between the generator 16 andthe liquid held in the bag B.

As illustrated, the bag B associates intimately with the at least partlyconductive container 14 and is filled with the selected liquid or otherconductive fluid in need of mixing during the course of bioprocessing.One pole of the generator 16 is electrically connected to the electrode12 at the outer (non-sterile) end. The other pole of the generator 16 iselectrically connected to the conducting container 14 including the bagB. The electric current is measured in the circuit (which of course isnormally open in the illustrated embodiment) using the detector 18.

If there is no leak through the wall of the bag B, there is noelectrical continuity and thus no flow of electric current. In otherwords, the circuit including the electrode 12, container 14, generator16, and detector 18 remains open. Electric current is not detected orregistered, thus indicating a “no leak” state.

However, if a perforation or hole in the bag wall exists, the leakingliquid (note arrow L in FIG. 2) forms an electrical contact between theliquid in the bag B and container 14. This results in closed circuitthrough which electric current can flow from the generator 16 to thedetector 18, which indicates the presence of the leak. Although notnecessary for most applications, it may also be advantageous to pre-wetthe exterior surface of the bag B, as this will help to ensure that thecircuit is closed by even the smallest of leaks.

In the preferred embodiment, this detector 18 comprises a currentmeasuring device, such as an amp meter (in which case one of the pole ofthe generator 16 connects to the electrode 12 or to the container 14, asshown in FIG. 2). However, any suitable indicator to alert a user to theleak, such by creating a visual or aural signal, may be used. Theimportant point is that the presence of the leak is properly andpromptly identified such that suitable ameliorative measures may betaken.

As should be appreciated, the generator 16 and detector 18 may beincorporated in one device (not shown). This device can simply measurethe resistance of the circuit (which can of course be open or closed).In case of no leak (an open circuit), the resistance is very high.However, in case of a leak closing the circuit, the resistance wouldsharply drop and thereby indicate the presence of the leak.

As should be further appreciated, the electrode 12 can be pre-introducedduring manufacturing, in which case it would become an integral part ofthe bag B. Accordingly, the electrode 12 should be capable to withstandthe sterilization cycle performed on the bag B, such as Gamma radiationsterilization. Another options to sterilize the electrode 12 separatelyand introduce it via a tube T associated with a sterile connectiondevice K (such as a KLEENPACK device of all Corporation or a BIOQUATEaseptic disposable connector, manufactured by BioQuate Inc.). In suchcase, as shown in FIG. 3, the electrode 12 may not project into theinterior compartment of the bag B, despite making contact with the fluidF by way of the tube T.

As contrasted with external leaks, internal leaks develop when only oneor several layers of material (e.g., plastic film) have holes orperforations, but the external layer remains intact. In this situation,the fluid may be not coming out of the bag to the external environment,but rather may accumulates between the layers. To detect this kind ofleak, a leak detection apparatus 100 in accordance with another aspectof the invention is described.

In the preferred second embodiment of the apparatus 100 for detectinginternal leaks now being described, and with reference to FIG. 4, asensor is associated with and preferably arranged between at least twointernal and external layers of material forming L₁, L₂ of the bag B(which layers are normally in intimate contact, but are shown spacedapart for purposes of illustration). In one particularly preferredembodiment, as shown in FIG. 3 (in which the proportions may beconsidered altered for purposes of illustration), this sensor comprisesat least two electrodes 102 a, 102 b that are spaced apart or otherwisenot in electrical contact in the absence of a leak. This may beaccomplished by separating the electrodes 102 a, 102 b by an insulator102 c (which if the second electrode 102 b comprises a conductivesupport structure, like container 14, could be considered the bag B).

Preferably, as shown, the electrodes 102 a, 102 b are both between thelayers L₁, L₂, but penetrate the external layer L₂ only. In other words,no part of the sensor is in contact with the interior of the bag B,which thus helps to ensure and maintain the desired sterile environment.Most preferably, the sensor is located along or adjacent a bottomportion of the bag B for reasons that will be better understood uponreviewing the following description.

As before, the apparatus 100 with the sensor further includes agenerator 116 capable of generating DC (Direct current) or AC(Alternating current) voltage; and (2) a detector 118 capable ofdetecting DC or AC electric current. Suitable connections, such as bywires, interconnect the electrodes 102 a, 102 b, generator 116, anddetector 118 so as to form a circuit (and preferably one that remainsopen in the absence of a leak from the internal layer L₁ in view of theinitially isolated electrodes 102 a, 102 b).

In using this embodiment and a corresponding method, the sensor isinitially such that no internal leak is detected. If the liquid leaksthrough the first (liquid touching) layer L₁ of the bag B, it may flowdown toward the bottom portion of the bag B and make contact theelectrodes 102 a, 102 b. Such contact closes the electric circuit suchthat current flow is established. Consequently, the detector 118indicates the presence of the leak, such as by indicating the flow ofelectric current.

Summarizing the foregoing, apparatus 10 or 100 can be used to advantagein connection with bioprocessing applications where fluid conductors,such as electrically conductive biological fluids (typically liquids),are at least temporarily held in thin-walled, flexible or collapsiblevessels, such as for example disposable bags made of one or more layersof plastic film. A sensor includes electrodes 12, 14 or 102 a, 102 bthat may be connected by a leak, either internal to a multi-layeredvessel or external thereto, to a generator 16, 116. An associateddetector 18, 118 can detect the presence of the leak to allow forappropriate corrective action, thereby saving time and money.

The foregoing descriptions of various embodiments of the inventions arepresented for purposes of illustration and description, and are notintended to be exhaustive or limiting. Modifications are possible inview of the teachings provided herein. For instance, the invention couldbe used in an arrangement where the sensor associated with the flexiblevessel forms part of a normally closed circuit whereby the leak createsa short and thus opens the circuit. Additionally, both apparatus 10 andapparatus 100 may together for detecting internal and external leaks.More than one sensor may also be provided in either apparatus 10, 100.Also, instead of forming all or part of a container 14 serving as asupport structure, the second electrode of the apparatus 10 may comprisea conducting mesh or like reticulated structure external to the bag B oranother structure integrally formed with the bag (such as a metallizedfilm). Although specifically proposed for use with a flexible plasticbag, the apparatus 10, 100 may be used in connection with any vesselhaving an interior compartment susceptible to leaking. The embodimentsdescribed provide the best illustration of the principles of theinvention and its practical applications to thereby enable one ofordinary skill in the art to utilize the invention in variousembodiments and with various modifications as are suited to theparticular use contemplated.

1. An apparatus intended for use in at least temporarily holding anelectrically conductive fluid in need of processing under sterileconditions, comprising: a plastic bag having a first interiorcompartment capable of receiving the conductive fluid for processingunder sterile conditions; a rigid container having a second interiorcompartment for at least partially receiving and supporting the bag; anda sensor for sensing the presence of a leak of the conductive fluid fromthe first interior compartment, said sensor comprising first and secondelectrodes, wherein the first electrode associates with an opening tothe first interior compartment of the bag and said second electrode isarranged external to the first interior compartment for completing anelectrical connection with the first electrode in the presence of theleak.
 2. The apparatus of claim 1, wherein the sensor further includes agenerator of AC or DC voltage and a detector connected to the first andsecond electrodes for detecting current in the resulting circuit whenconnected by the leak.
 3. The apparatus of claim 1, wherein the firstelectrode projects through a hermetic seal associated with a sidewall ofthe bag.
 4. The apparatus of claim 1, wherein the rigid supportcontainer at least partially comprises a conductive material forming thesecond electrode.
 5. The apparatus of claim 1, wherein the bag includesa tubular port for receiving the first electrode.
 6. The apparatus ofclaim 5, wherein the tubular port includes a connector for allowing thefirst electrode to contact the conductive fluid under sterileconditions.
 7. The apparatus of claim 1, wherein the bag comprises afirst layer of material arranged for forming the first interiorcompartment and a second layer of material adjacent the first layer ofmaterial.
 8. The apparatus of claim 7, wherein the sensor comprisesfirst and second electrodes are positioned at least partially betweenthe first and second layers of material.
 9. The apparatus of claim 7,wherein one of said first and second electrodes comprises the secondlayer of material of the bag.
 10. An apparatus intended for use in atleast temporarily holding an electrically conductive fluid in need ofprocessing under sterile conditions and detecting a leak thereof,comprising: a plastic processing bag having a first interior compartmentcapable of receiving the conductive fluid under sterile conditions; anat least partially conductive support structure having a second interiorcompartment for at least partially receiving the plastic processing bag;and an electrode connected to the conductive fluid in the first interiorcompartment and arranged to form an electrical circuit with theconductive support structure in the presence of the leak.
 11. Theapparatus of claim 10, further including a generator of AC or DC voltageand a detector connected to the electrode and the conductive supportstructure for detecting a current in the electrical circuit.
 12. Anapparatus intended for use in at least temporarily holding anelectrically conductive fluid in need of processing and detecting a leakthereof, comprising: a processing vessel comprising a first layer offlexible material creating an interior compartment capable of receivingthe conductive fluid under sterile conditions and a second layer offlexible material adjacent the first layer; first and second electrodesarranged external to the interior compartment for completing anelectrical connection with the first electrode in the presence of theleak, at least said first electrode extending at least partially betweenthe first and second layers of flexible material, wherein said secondlayer of flexible material and the second electrode are unitary.
 13. Theapparatus of claim 12, wherein both of said first and second electrodesare between the first and second layers of flexible material.
 14. Theapparatus of claim 12, wherein said second electrode comprises a rigidcontainer for receiving and supporting the processing vessel.
 15. Amethod of processing fluid under sterile conditions, comprising:providing a processing bag having a first interior compartment creatinga sterile environment; providing the bag with a support structure havinga second interior compartment; providing an electrically conductivefluid in the interior compartment; and providing first and secondelectrodes capable of being connected by the leak, creating anelectrical potential difference across the electrodes, and detecting thecurrent flowing through the circuit formed by the presence of the leak,wherein the support structure is at Least partially conductive, and thestep of providing first and second electrodes comprises providing thefirst electrode in contact the conductive fluid in the first interiorcompartment and using the support structure as the second electrode. 16.The method of claim 15, wherein the bag comprises first and secondlayers of material, and the providing step comprises positioning thefirst and second electrodes external to the first interior compartmentand at least partially between the first and second layers of material.17. An apparatus intended for use in at least temporarily holding anelectrically conductive fluid in need of processing under sterileconditions, comprising: a flexible vessel having a first interiorcompartment capable of receiving the conductive fluid for processingunder sterile conditions, said vessel comprising a first layer ofmaterial arranged for forming the first interior compartment and asecond layer of material adjacent the first layer of material; a rigidcontainer having a second interior compartment for at least partiallyreceiving and supporting the flexible vessel; and a sensor for sensingthe presence of a leak of the conductive fluid from the first interiorcompartment, wherein the sensor further comprises first and secondelectrodes, one of said first and second electrodes comprising thesecond layer of material of the vessel.
 18. An apparatus intended foruse in at least temporarily holding an electrically conductive fluid inneed of processing and detecting a leak thereof, comprising: aprocessing vessel comprising a first layer of flexible material creatingan interior compartment capable of receiving the conductive fluid understerile conditions and a second layer of flexible material adjacent thefirst layer; first and second electrodes arranged external to theinterior compartment for completing an electrical connection with thefirst electrode in the presence of the leak, at least said firstelectrode extending at least partially between the first and secondlayers of flexible material, wherein said second electrode comprises arigid container for receiving and supporting the vessel.
 19. Theapparatus of claim 10, wherein the at least partially conductive supportstructure comprises a layer of the processing bag.